In the control of transcription in eukaryotic cells, it is generally expected that sequence-specific DNA-binding proteins will play a key role, as they do in bacterial systems. This project proposes the isolation of proteins which will bind to rat ribosomal DNA (rDNA), which will be cloned in bacterial cells using recombinant-DNA techniques. The proteins isolated will be analyzed by two-dimensional polyacrylamide gel electrophoresis, for heterogeneity; and nitrocellulose filter-binding assays, for sequence-specific binding to rDNA. Later studies will determine the effects of such proteins on the transcription of preribosomal RNA in isolated nucleoli, and their possible intracellular functions, by comparison of similar proteins in related nucleolar systems. Since some of the hepatoma cells which will be studied in this work transcribe pre-rRNA at a rate 10 times or more that of the related normal rat liver cells, it is hoped that the mechanisms which allow the tumor cells to support their growth in this way can be discovered, and that this knowledge might eventually be applied in suppression of the growth of the tumors. The techniques developed in these studies should also be applicable to the study of transcriptional control in single-copy structural genes.